[PATCH v2] kvm: x86: Add logical CPU to KVM_EXIT_FAIL_ENTRY info

[Jim Mattson <jmattson@google.com>]

More often than not, a failed VM-entry in a production environment is
the result of a defective CPU (at least, insofar as Intel x86 is
concerned). To aid in identifying the bad hardware, add the logical
CPU to the information provided to userspace on a KVM exit with reason
KVM_EXIT_FAIL_ENTRY. The presence of this additional information is
indicated by a new capability, KVM_CAP_FAILED_ENTRY_CPU.

Signed-off-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Oliver Upton <oupton@google.com>
Cc: Liran Alon <liran.alon@oracle.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
---
 Documentation/virt/kvm/api.txt | 1 +
 arch/x86/kvm/svm.c             | 1 +
 arch/x86/kvm/vmx/vmx.c         | 2 ++
 arch/x86/kvm/x86.c             | 1 +
 include/uapi/linux/kvm.h       | 2 ++
 5 files changed, 7 insertions(+)

diff --git a/Documentation/virt/kvm/api.txt b/Documentation/virt/kvm/api.txt
index ebb37b34dcfc..6e5d92406b65 100644
--- a/Documentation/virt/kvm/api.txt
+++ b/Documentation/virt/kvm/api.txt
@@ -4245,6 +4245,7 @@ hardware_exit_reason.
 		/* KVM_EXIT_FAIL_ENTRY */
 		struct {
 			__u64 hardware_entry_failure_reason;
+			__u32 cpu; /* if KVM_CAP_FAILED_ENTRY_CPU */
 		} fail_entry;
 
 If exit_reason is KVM_EXIT_FAIL_ENTRY, the vcpu could not be run due
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 122d4ce3b1ab..e07c5ce3ac93 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -4980,6 +4980,7 @@ static int handle_exit(struct kvm_vcpu *vcpu)
 		kvm_run->exit_reason = KVM_EXIT_FAIL_ENTRY;
 		kvm_run->fail_entry.hardware_entry_failure_reason
 			= svm->vmcb->control.exit_code;
+		kvm_run->fail_entry.cpu = vcpu->cpu;
 		dump_vmcb(vcpu);
 		return 0;
 	}
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index e3394c839dea..17d1a1676fc0 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5846,6 +5846,7 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu)
 		vcpu->run->exit_reason = KVM_EXIT_FAIL_ENTRY;
 		vcpu->run->fail_entry.hardware_entry_failure_reason
 			= exit_reason;
+		vcpu->run->fail_entry.cpu = vcpu->cpu;
 		return 0;
 	}
 
@@ -5854,6 +5855,7 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu)
 		vcpu->run->exit_reason = KVM_EXIT_FAIL_ENTRY;
 		vcpu->run->fail_entry.hardware_entry_failure_reason
 			= vmcs_read32(VM_INSTRUCTION_ERROR);
+		vcpu->run->fail_entry.cpu = vcpu->cpu;
 		return 0;
 	}
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index cf917139de6b..9e89a32056d1 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3273,6 +3273,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_GET_MSR_FEATURES:
 	case KVM_CAP_MSR_PLATFORM_INFO:
 	case KVM_CAP_EXCEPTION_PAYLOAD:
+	case KVM_CAP_FAILED_ENTRY_CPU:
 		r = 1;
 		break;
 	case KVM_CAP_SYNC_REGS:
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index f0a16b4adbbd..09ba7174456d 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -277,6 +277,7 @@ struct kvm_run {
 		/* KVM_EXIT_FAIL_ENTRY */
 		struct {
 			__u64 hardware_entry_failure_reason;
+			__u32 cpu;
 		} fail_entry;
 		/* KVM_EXIT_EXCEPTION */
 		struct {
@@ -1009,6 +1010,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_PPC_GUEST_DEBUG_SSTEP 176
 #define KVM_CAP_ARM_NISV_TO_USER 177
 #define KVM_CAP_ARM_INJECT_EXT_DABT 178
+#define KVM_CAP_FAILED_ENTRY_CPU 179
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
-- 
2.24.1.735.g03f4e72817-goog